1. BU Astronomy Symposium
Planetary atmospheres and ionospheres… How does a solar energetic particle event disrupt the ionosphere of Mars?
Paul Withers
BU Astronomy Symposium
Boston, MA

2. What’s going on?
Katy Fallows – How does the lower ionosphere of Mars work? Zach Girazian – How does the main layer in the ionosphere of Mars work? Majd Matta – Numerical simulations of the ionosphere of Mars Rob Pratt – Response of the thermosphere of Mars to extreme events Nick Ferreri – Resurrecting ancient Mars data
Emphasis on working closely with spacecraft data Desire models that promote physical understanding, not complicated black box Diversification beyond Mars is planned

3. Ionospheres of Earth and Mars

4. The problem: MARSIS gets blacked out occasionally
Radio wave absorption
Excess plasma at
low-ish altitudes
Gurnett et al. (2005)
Morgan et al. (2006)

5. Happens during solar energetic particle (SEP) events
“High” means surface reflection
is visible
“Low” means it is not visible
Proxy for energetic particle
flux at Mars
Another proxy for the same thing
Hypothesis: SEP events cause sufficient
plasma enhancement at low altitudes
to account for MARSIS blackouts
But this has never been simulated…
DOY 2005

6. Model ingredients “Range” – How many g cm-2 of CO2
stops a proton of some energy
Energy spectrum
Number of protons
per cm-2 s-1 MeV-1
Picked a really big example
29 September 1989
Altitude at which a proton
of some energy is stopped
Neutral atmosphere

7. Model results Make an assumption for how energy is deposited
Black line – N(z) for SEP and photons
Grey line – N(z) for SEP only
Dashed line – Simple analytical
prediction for the grey line
Pretty good, huh?
Ask me about the wacky chemistry
below 70 km altitude…
Make another one for
associated ionization rate,
then get colleagues in India to
produce ionospheric densities

8. Major ionospheric changes
A – Unusually large electron densities at km
Should be visible in radio occultation observations ?
B – Increase in total electron content (TEC)
Is visible in MARSIS TEC observations !
C – Tremendous radio wave absorption
Sufficient to black out MARSIS surface reflections !

9. Backup

10. SEP only, positive ions

11. SEP only, negative ions

12. SEP and photons, positive ions

13. SEP and photons, negative ions